(1) Field of the Invention
This invention relates to a reformer for hydrogen generation, suitably used in industries and vehicles.
(2) Description of the Related Art
In recent years, production of electricity without causing environmental pollution has drawn attention and an interest in fuel cell has increased. Fuel cell has various advantages such as high efficiency in power generation, formation of small amount of carbon dioxide (CO2) and substantially no formation of harmful substances such as carbon monoxide (CO), nitrogen oxides (NOx) or the like. Therefore, researches and developments on use of fuel cell in on-site type power generator or automobile have been under way recently. In generating electricity using a fuel cell, high-purity hydrogen is required. This hydrogen is produced by using, as a starting material, a hydrocarbon (e.g., butane or propane), an alcohol (e.g., methanol), CO or the like and conducting a catalytic reaction.
The main reaction in the above hydrogen production is steam reforming which takes place in the presence of steam and a catalyst. In the gas produced by steam reforming, however, hydrogen has not a sufficient purity to be used in a fuel cell, and CO which is a coproduct of hydrogen has a deactivating effect on Pt-based electrode used in the fuel cell. Therefore, a CO shift reaction (an aqueous conversion reaction) and a selective CO oxidation reaction are conducted to increase hydrogen purity.
As still another process for generating hydrogen from a hydrocarbon or the like, there is a process which comprises generating hydrogen and CO by a partial oxidation reaction of a hydrocarbon in place of the above-mentioned steam reforming and then conducting the above-mentioned CO shift reaction and CO selective oxidation reaction to obtain hydrogen. As still another process for generating hydrogen from a hydrocarbon or the like, there is a process using a decomposition reaction. A specific example of the decomposition reaction is a decomposition reaction for generating hydrogen from methanol.
It is known, in the reformer for producing hydrogen based on the above reactions, that one of suitable reactor configurations is disposition of a plurality of catalyst units in the flow path for individual reactions, such as steam reforming, CO shift reaction and selective CO oxidation. However, the relationship between these catalyst units with respect to heat capacity has not been fully investigated for the reformer in which two or more catalyst units are disposed.
Attempts have been done to use a honeycomb structure for each of the above catalyst units. However, the relationship between these catalyst units with respect to cell density has not been fully investigated for the reformer in which two or more catalyst units are disposed.
The present invention is developed to improve the above situations. It is an object of the present invention to improve safety, heating characteristics during the start-up period, efficiency of hydrogen production and reduction in production of CO as the coproduct for a reformer in which two or more catalyst units are disposed in the flow path by improving the relationship between these catalyst units with respect to heat capacity.
It is another object of the present invention to improve, e.g., efficiency of hydrogen production and reduction in production of CO as the coproduct for a reformer in which two or more catalyst units of a honeycomb structure are disposed in the flow path by improving the relationship between these catalyst units with respect to cell density, in particular in consideration of the case where the reaction taking place in the catalyst unit is essentially exothermic or endothermic to release or absorb a large quantity of heat, or where the reactant is charged into the reactor at a high concentration.
It is still another object of the present invention to improve, e.g., efficiency of hydrogen production and reduction in production of CO as the coproduct for a reformer in which two or more catalyst units of a honeycomb structure are disposed in the flow path by improving the relationship between these catalyst units with respect to cell density, in particular in consideration of the case where the reaction taking place in the catalyst unit is not so fast as combustion, or where the reactant stream contains a poisonous material to the catalyst, e.g., gasoline.
According to the present invention, there is provided, as a first invention,
a reformer disposed in the flow path of a reactant fluid, which comprises two or more catalyst units capable of generating hydrogen from a reactant fluid containing an organic compound or carbon monoxide, by catalysis,
wherein, at least two of the above catalyst units satisfy the following relationship:
Heat capacity of the upstream catalyst unitxe2x89xa6Heat capacity of the downstream catalyst unit
Furthermore, according to the present invention, there is provided, as a second invention,
a reformer disposed in the flow path of a reactant fluid, which comprises two or more catalyst units of a honeycomb structure capable of generating hydrogen from a reactant fluid containing an organic compound or carbon monoxide, by catalysis,
wherein, at least two of the above catalyst units satisfy the following relationship:
Cell density of the upstream catalyst unitxe2x89xa6Cell density of the downstream catalyst unit
Furthermore, according to the present invention, there is provided, as a third invention,
a reformer disposed in the flow path of a reactant fluid, which comprises two or more catalyst units of a honeycomb structure capable of generating hydrogen from a reactant fluid containing an organic compound or carbon monoxide, by catalysis,
wherein, at least two of the above catalyst units satisfy the following relationship:
Cell density of the upstream catalyst unitxe2x89xa7Cell density of the downstream catalyst unit.
In the present invention, xe2x80x9ca catalyst unit of generating hydrogen from a reactant fluid containing an organic compound or carbon monoxide, by catalysisxe2x80x9d includes a catalyst unit which shows a catalytic reaction of increasing purity of hydrogen generated from a reactant fluid containing an organic compound or carbon monoxide, by catalysis, e.g., CO shift reaction and selective oxidation of CO. Also in the present invention, the term xe2x80x9choneycomb structurexe2x80x9d means a structure having a number of through-holes (cells) separated by a partition from each other.